Hydroxyfasudil, an active metabolite of fasudil hydrochloride, relaxes therabbit basilar artery by disinhibition of myosin light chain phosphatase

Fasudil hydrochloride (AT877, hexahydro-1-(5-isoquinolinesulfonyl)-1H-1,4-d iazepine hydrochloride, identical to HA1071) inhibits cerebral vasospasm af ter subarachnoid hemorrhage in experimental animals and humans. In the curr ent study, the vasorelaxing mechanism of hydroxyfasudil, a hydroxylated met abolite of fasudil hydrochloride, was determined in the rabbit basilar arte ry. The effects of hydroxyfasudil on tension, intracellular Ca2+ concentrat ion ([Ca2+](i)), and phosphorylation of the myosin light chain were examine d using the isolated and intact or permeabilized rabbit basilar artery with out endothelium in vitro. In the intact rabbit basilar artery, hydroxyfasud il elicited a concentration-dependent relaxation of the artery precontracte d with 1 nmol/L endothelin-1 (ET-1) plus 20 mmol/L KC1 without any signific ant decrease in [Ca2+](i) as determined by fura-2 microfluorometry (IC50: 5 .1 +/- 4.6 mu mol/L). The relaxation induced by hydroxyfasudil was accompan ied with dephosphorylation of the myosin light chain. In the permeabilized preparation, hydroxyfasudil inhibited the contraction induced by ET-1, guan osine 5 ' -O-(3-thiotriphosphate), or the catalytic subunit of rho-associat ed kinase, but it did not inhibit Ca2+-induced contraction under the condit ion of inhibited myosin light chain phosphatase. Hydroxy fasudil showed a g reater relaxant effect under decreased adenosine triphosphate (ATP) levels. The present study indicated that hydroxyfasudil relaxes the rabbit basilar artery mainly by disinhibiting myosin light chain phosphatase through the inhibition of rho-associated kinase and that this effect depends on the int racellular ATP concentration.